The World Health Organization (WHO) recently reported that obesity has become a global epidemic, posing a serious threat to public health because of the increased risk of associated health problems (See Report of a WHO Consultation on Obesity: Obesity-Preventing and Managing a Global Epidemic; World Health Organization: Geneva, 1997). Obesity is characterized by excess body fat, especially visceral fat, and constitutes a pro-inflammatory state eventually leading to serious health consequences. There are growing evidences that obesity as a chronic disease cannot be cured by short-term dieting or exercise alone, but additional pharmacological treatments would lead to higher success rates.
CB1 cannabinoid receptor belongs to G-protein-coupled receptor (GPCR) type and is coupled to inhibitory G proteins (G(i/o)) to inhibit certain adenylyl cyclase isozymes, leading to decreased cAMP production, decreased Ca2+ conductance, increased K+ conductance, and increased mitogen-activated protein kinase activity (See Di Marzo et al., Nat. Rev. Drug Discovery 2004, 3, 771-784; Rhee, M. H. et al., J. Neurochem. 1998, 71, 1525-1534). The major physiological effect of cannabinoids (in the central nervous system (CNS) and neuronal tissues) is the modulation of neurotransmitter release via activation of presynaptic CB1 receptors located on distinct types of axon terminals throughout the brain (See Howlett, A. C. et al., Neuropharmacology 2004, 47 (Suppl. 1), 345-358).
The CB1 receptor is mainly expressed in several brain areas including the limbic system (amygdala, hippocampus), hypothalamus, cerebral cortex, cerebellum, and basal ganglia. In the cerebellum and basal ganglia cannabinoids modulate the locomotor activity. In the limbic system, cannabinoids influence learning, memory, emotion, and motivation, and through activation of CB1 receptors in the limbic system-hypothalamus axis, cannabinoids have an important role in the control of appetite. Moreover, lower levels of CB1 receptors can also be found in peripheral tissues including urinary bladder, testis, prostate, GI tract, heart, lung, adrenal gland, parotid gland, bone marrow, uterus, ovary, and adipose tissue (See Cota, D. et al., J. Clin. Invest. 2003, 112, 423-431; Ravinet Trillou, C. et al., Int. J. Obes. Relat. Metab. Disord. 2004, 28, 640-648; Galiegue, S. et al., Eur. J. Biochem. 1995, 232, 54-61; Howlett, A. C. et al., Pharmacol. Rev. 2002, 54, 161-202).
Many preclinical in vitro and in vivo experiments have shown that CB1 receptor antagonists can influence energy homeostasis by central and peripheral mechanisms and may represent promising targets to treat diseases that are characterized by impaired energy balance. Already the first published studies with rimonabant (SR141716) in both rodents (See Amone, M. et al., Psychopharmacology (Berlin) 1997, 132, 104-106) and primates (See Simiand, J.; Keane, M.; Keane, P. E.; Soubrie, P. Behav. Pharmacol. 1998, 9, 179-181) showed clear differentiation, i.e., marked effects on sweet food intake versus marginal effects on regular chow intake or water drinking. Many other preclinical “proof of concept” studies have been performed in the meantime with several CB agonists and antagonists to further uncover the amount and mode of contribution of cannabinergic system modulators to energy homeostasis. Almost all of those studies have been recently reviewed (See Smith, R. A. et al., IDrugs 2005, 8, 53-66).
Considering the important impact of obesity on public health and the lack of any efficient and viable drug to cure it, it is no surprise that CB1 antagonists are currently the subject of intense studies, which were published in several reviews (See Adam, J. et al., Expert Opin. Ther. Patents, 2002, 12(10), 1475-1489; Hertzog, D. L. Expert Opin. Ther. Patents, 2004, 14(10), 1435-1452; Lange, J. H. M. et al., Drug Discov. Today, 2005, 10, 693-702; Bishop, M. J. J. Med. Chem., 2006, 49(14), 4008-4016).